The polycarbonate diol diacrylate is a compound useful as a starting material for ink, a paint, a coating material, an adhesive, a photocurable resin, a cross-linking agent, an electrolyte material, and other resins, etc. For example, in Patent Literature 1, there is disclosed an optical waveguide in the form of a film using a polycarbonate diol diacrylate.
As a method for preparing a polycarbonate diol diacrylate, it has been known a method wherein a polycarbonate diol and an acrylic acid are reacted in the presence of a protonic acid catalyst such as p-toluenesulfonic acid, etc. (for example, see Patent Literature 2).
However, according to this method, there is a serious problem that the resulting polycarbonate diol diacrylate is colored to brown color which is concerned with the quality of the product. Moreover, according to this method, acrylic acid as a starting material is used excessively, so that even when it is removed by neutralization and washing after the synthesis, an acid catalyst, a sulfur component caused by the starting material, or impurities remain in the resulting product, whereby there is a problem that worsening of the quality of the product (bad smell, metal corrosion) is likely caused.
It has been also known a process for preparing a polycarbonate diol diacrylate wherein a polycarbonate diol and an acrylic acid ester compound are reacted in the presence of an organometallic catalyst while removing a forming alcohol (for example, see Patent Literature 3). However, according to this method, the forming alcohol may exchange to the carbonate bond in the polycarbonate diol to form an alkoxy terminal. The alkoxy terminal lowers the cross-linking density of the cured product in the later curing step, so that the formation thereof shall be desirably avoided. In addition, residue of the metal component derived from the organometallic catalyst can affect the quality of the product, so that decomposition and recovering steps of the catalyst component are required. Moreover, according to this method, when the by-produced alcohol is distilled off, there is a problem that the starting acrylic acid ester is azeotroped with the alcohol and distilled out from the reaction system. In addition, there is a problem that a popcorn polymerization due to vaporized starting acrylic acid ester may be caused.
Here, the popcorn polymerization is a phenomenon that forms a polymer which becomes a core mainly in a vapor phase, and causes polymerization explosively from the polymer as a starting point accompanying with a high temperature heat of polymerization, and forms a porous bulky polymerized product. If the popcorn polymerization occurred during a large scale preparation process, there is a fear that it may cause clogging of the apparatus which leads breakage of the facilities and explosion of the same, so that a preparation process which can prevent from increase in a vinyl compound concentration and can carry out at a low temperature has been desired.
It has been known as a method for acrylating the free hydroxyl group at a relatively lower temperature without using an acid catalyst or a metal component, a method of using a lipase as an enzymatic catalyst (for example, see Non-Patent Literature 1). Also, it has been reported that it is possible to produce an acrylic acid ester in a non-polar solvent by using vinyl acrylate and an immobilized lipase (for example, see Non-Patent Literature 2). However, it has never been known an example in which acrylation is carried out by using a polycarbonate diol as a substrate and a lipase.